<p><b>Abstract</b>—The problem of merging <it>k</it> (<it>k</it>≥ 2) sorted lists is considered. We give an optimal parallel algorithm which takes <tmath>$O({\textstyle{{n\log k} \over p}}+\log n)$</tmath> time using <it>p</it> processors on a parallel random access machine that allows concurrent reads and exclusive writes, where <it>n</it> is the total size of the input lists. This algorithm achieves <it>O</it>(log <it>n</it>) time using <tmath>$p={\textstyle{{n\log k} \over {\log n}}}$</tmath> processors. Most of the previous research for this problem has been focused on the case when <it>k</it> = 2. Very recently, parallel solutions for the case when <it>k</it> > 2 have been reported. Our solution is the first logarithmic time optimal parallel algorithm for the problem when <it>k</it>≥ 2. It can also be seen as a unified optimal parallel algorithm for sorting and merging. In order to support the algorithm, a new processor assignment strategy is also presented.</p>